1. Field of the Invention
The invention relates to a high-voltage generator which includes a high-voltage unit for generating an output DC high voltage, and a voltage generating unit for generating at least one further, lower DC high voltage, the voltage generating unit receiving a DC voltage from the high-voltage unit, and including an adjustment unit for adjusting the further DC high voltage in a voltage range between a lower and an upper limit voltage.
2. Description of the Related Art
A high-voltage generator of this kind is known from U.S. Pat. No. 4,788,591. Therein, an output DC high voltage for feeding the anode of a picture tube is generated by means of a diode split transformer. Via an adjustment unit with two potentiometers, two voltages are generated so as to focus the electrons in the picture tube. The potentiometers are used to adjust these voltages in a range between a lower and an upper limit voltage which generally amount to 20% and 29%, respectively, of the output DC voltage in the case of a picture tube. One of the series-connected potentiometers is connected to a connection point of the high-voltage unit which carries a DC voltage. The base of the second potentiometer is connected to a DC voltage potential of 210 V which generally serves as a reference potential in a picture tube.
The dimensions and cost of a voltage generating unit in which adjustable DC high voltages are generated, for example, for the focusing of electrons in a tube, notably a picture tube, are determined essentially by the required electric strength and by the power loss of the adjustment unit which includes two potentiometers in the known device. In the case of a picture tube in which the output DC high voltage amounts to, for example, 25 kV so that the lower and the upper limit voltage amount to approximately 5 kV and 7.25 kV, respectively, the adjustment unit must have a high electric strength. In the known device, in which two series-connected potentiometers are arranged between a high-voltage potential of the high-voltage unit and a low-voltage potential which acts as a reference potential, the potentiometers must have a high electric strength, leading to high power losses, high costs and large dimensions of the potentiometers.